EP0385432A2 - Method for producing a three-dimensionally shaped, resin coated textile material and use of same - Google Patents

Abstract

A method is described for producing a dimensionally stable, three- dimensionally shaped, resin-coated sheet-like textile material, in which one or more layers of a thermoformable textile material, preferably of a knitted fabric, and one or more resin films are stacked one on top of the other and the stack is brought into the desired shape by thermoforming at a temperature at which the resin becomes free-flowing, the temperature being set for the resin to be able to harden and the shaped stack held in this shape for as long as it takes for the resin to harden completely or to a sufficient extent. <IMAGE>

Description

The present invention relates to a process for producing a dimensionally stable, three-dimensionally shaped, resin-coated, sheet-like textile material, the deformed structures obtained by this process and their use as core material in the production of sheet-like sandwich bodies.

Sheet-like sandwich bodies consisting of a core and two cover layers, the core of which has dimensionally stable, three-dimensionally deformed textile materials, are already e.g. known from FR-A-23 25 503 and EP-A-158 234. The sandwich material described in these publications has a core made of a three-dimensionally deformed, flat textile material which has a large number of elevations with the same height and flat plateau on a base surface in a regular arrangement. There are considerable differences between the core materials known from FR-A-23 25 503 and EP-A-158 234 with regard to their structure. While the materials known from FR-A-23 25 503 show an essentially completely closed structure, in which both the textile base areas and the walls of the elevations distributed on the base area form a solid, pore-free, fiber-infused resin composition, which constitute the EP-A 158 234 known core materials represent a network structure made of resin-impregnated threads with open meshes.

The core material with closed structure known from FR-A-2 325 503 is produced by pressing a resin-impregnated staple fiber fabric into one Mold of the desired geometric shape. Relative to the fiber weight, a relatively high amount of resin is used, so that an essentially fiber-reinforced resin molded body results after pressing.

The core material thus obtained has a relatively high weight. It does not allow gas exchange and it shows little flexibility.

The network-structured core material known from EP-A-158 234 (hereinafter also referred to as filigree-structured) is produced by deep-drawing a deep-drawable textile material impregnated with relatively little resin, e.g. a resin-impregnated knitted fabric (knitted fabric, knitted fabric). This core material known from EP-A-158 234 has a low density with good mechanical stability. It allows free gas exchange between the sides of the surface and is highly flexible.

As already stated above, the core material known from EP-A-158 234 is produced by impregnating a sheet-like textile material with a thermoplastic or thermosetting resin, drying the impregnated material into a so-called prepreg and then deforming the prepreg to the desired shape of the core material a deep drawing process.

A serious disadvantage of this manufacturing process is that it is very difficult to uniformly impregnate a deep-drawable sheet-like textile material with a resin without the material being fully or partially pre-stretched. Such a, possibly uneven, warping of the textile surface has a lack of deep-drawing ability and in the finished product a, possibly partial, reduction the fiber strength. The handling of the not yet precondensed, resin-impregnated, deep-drawable textile material can easily lead to a partial pre-stretching of this material, with the above-mentioned disadvantages for the uniformity of the quality of the end product, unless special precautions are taken. To some extent, these manufacturing problems stand in the way of the widespread use of these core materials, which are intrinsically inexpensive. The present invention overcomes the disadvantage of this known manufacturing process.

The present invention thus relates to a method for producing a dimensionally stable, three-dimensionally shaped, resin-coated, sheet-like textile material, which is characterized in that one or more layers of a thermoformable textile material and one or more resin films are stacked on top of one another, the stack at a temperature at which the Resin flowable is brought into the desired shape by a molding process, and then the temperature is set so that the resin can harden and the shaped stack is kept in the desired shape until the resin is completely or sufficiently hardened, whereby The term "sufficiently hardened" should be understood to mean that the resin in this state is able to stabilize the deformed fabric in the desired shape after opening the deep-drawing tool.

FIG. 1 schematically illustrates a dimensionally stable, three-dimensionally shaped, resin-coated sheet-like textile material (1) produced according to the invention, which has a plurality of elevations (3) on a base area (2). In the elevations in particular, the figure shows a reticulated filigree structure obtained by stretching the base material.

In principle, any sheet-like textile material is considered as a deep-drawable textile material, the stretchability of which enables the partial increase in surface area occurring during deep-drawing without tearing the textile material. As already stated in EP-A-158 234, knitted fabrics such as e.g. Knitted or knitted fabrics in which the stretchability results from the deformability of the mesh structure. It has also already been proposed to produce deep-drawable textile fabrics from wrapping yarns, which consist of a thread-like core material which is wrapped by a sheath thread that is 1.5 to 3 times, preferably 1.8 to 2.2 times longer is as the core material. A sheet-like textile material made from such a wrapping yarn can be in the form of a woven fabric, a knitted fabric, a knitted fabric, a scrim or a nonwoven reinforced by wrapping threads. When deep-drawing such a material, the core threads are torn in a statistically distributed manner in the areas to be deformed, thereby releasing a corresponding length of the covering thread. This mechanism enables a considerable increase in area during the deep-drawing process without destroying the entire area. It is particularly preferred to use a wrapping yarn whose core threads have a lower stability than the sheath filaments, i.e. that the core thread is destroyed in the mechanical and possibly also thermal stress occurring during deep drawing and / or by the influence of chemicals, while the sheath thread is stretched and assumes the supporting function in the fabric.

Further suitable as deep-drawable textile materials are those which have a high, non-elastic deformability, such as, for example, from GB-A-2 176 511 and Derwent papers 87-025859 / 04 and 87-040235 / 06 of Japanese Patent Publications 61-282452 and 61-296152 are known. These known three-dimensionally deformable textile materials are produced by subjecting corresponding sheet-like textile materials made of synthetic fibers to heat-shrinkage treatment and thereby imparting them non-elastic extensibility, or by producing these textile materials from the start from yarns which already have non-elastic extensibility. Non-elastically stretchable yarns are described, for example, in DE-A-28 21 243 and DE-C-35 21 469.

The thread material from which the deep-drawable textile fabric is made is not subject to any restrictions; Both knitted fabrics and the deep-drawable textile materials made from wrapping yarns can consist of continuous filament yarns as well as of spun yarns. However, ribbon threads or splice ribbon threads can also be used, for example. The same applies to the chemical nature of the thread material. In principle, it is possible for the deep-drawable textile material to consist of a covering yarn or of a knitted fabric made of natural fibers, synthetic fibers or inorganic fibers or continuous filaments, such as glass fibers. In view of the better variability of the strength properties of the material, in particular in the finally deformed state, it is advantageous, however, that the textile material be constructed from synthetic fibers. If, on the other hand, the flame retardancy or flame retardancy of the material is in the foreground, it is preferred to use knitted fabrics made of inorganic fibers. Synthetic materials that can be considered are, for example, polyalkylenes, polyamides, polyesters or polyacrylonitrile. Polyester materials, in particular high-strength types, are particularly preferred for knitted fabrics, deep-drawable textile materials made from wrapping yarn preferably contain wrapping threads whose core threads with lower stability consist of polyalkylene or aliphatic polyamides and whose covering threads, which determine the final strength and stability of the three-dimensional element deformed by deep drawing, of aromatic polyesters, aromatic polyamides or polyacrylonitrile, in particular from the high-strength ones Types exist.

The resin films to be used in the method according to the invention can consist of thermoplastic or thermosetting resins (also referred to below as matrix material). The thermoplastic or thermosetting resin used is one which can stiffen the sheet-like textile material so that it becomes self-supporting. Thermosets are therefore particularly preferred, ie those resins which cure at elevated temperature with crosslinking to form an infusible material of high rigidity. Known resins of this type are, for example, unsaturated polyester resins (alkyd resins), mixtures of unsaturated polyesters with unsaturated monomeric compounds such as, for example, styrene, epoxy resins, phenolic resins or melamine resins. These resins are marketed and applied in the uncrosslinked state, in which they are still meltable and flowable at elevated temperature. The films to be used according to the invention from these still uncrosslinked resins have a thickness of approximately 50 to 500 μm, preferably 100 to 500 μm and a basis weight of approximately 50 to 500 g / m², preferably 100 to 500 g / m²
Of course, it is also possible to use thinner or thicker resin films with a correspondingly lower or higher basis weight for special purposes, for example for processing very fine or particularly thick textile materials. As a rule, these resin films already contain the crosslinking agent and necessary for crosslinking the resin the required polymerization catalyst and the appropriate accelerator substances.

Commercial resin films are often provided with a carrier to improve their mechanical stability. Resin films of this type are also very suitable for carrying out the process according to the invention. An example of commercially available resin films based on epoxy resin, which are available with or without a carrier and can be used according to the invention, is the Structufilm R 382 resin film ^(R) marketed by Hexcel SA.

To produce the three-dimensionally deformed textile material, one or more layers of the deep-drawable textile material and one or more resin films are laid in a suitable sequence on top of one another in a "stack". Accordingly, such a “stack” can also consist of a textile web and a resin film. The number of textile webs depends on the requirements placed on the strength of the core material to be manufactured. As a rule, no more than 4, preferably 1 or 2 textile webs, in particular a textile web, are used in a stack. The number of resin films in the stack depends on the desired degree of resin impregnation of the textile material. suitable coating quantities of the resin are in the range from 50 to 500, preferably from 100 to 300 g resin / m² of the textile material. Within the specified ranges, the amount of resin can be expediently adapted to the weight per square meter of the deep-drawable textile material. For example, when using a heavy textile material, you will work within the upper half of the specified ranges, with light textile materials in the lower half. For very special applications, it may be desirable to increase the amount of resin applied to such an extent that even when stretched Condition still a resin film remains between the threads of the textile network. However, it is preferred to measure the amount of resin so that the textile material forms a filigree network when stretched. If, for example, a textile material is to be impregnated with a resin layer of 200 g resin / m², a film of, for example, 0.2 mm thickness with a basis weight of 200 g / m² is placed in the stack to be deformed.

If several textile webs are to be provided in a stack to be deformed, the sequence of textile webs and resin films is expediently to be chosen such that, under the action of heat during the deep-drawing process, the resin can be distributed as evenly as possible into the textile surfaces. For thicker stacks, it is therefore expedient to use textile webs and resin films alternately. With a view to keeping the molding tool clean, it can also be advantageous to construct the stack in such a way that the top and bottom surfaces of the stack are formed by fabric webs and the necessary amount of resin is ensured by a corresponding number of resin films lying inside the stack. For example, a stack of 2 textile webs and 2 resin films can be constructed in the sequence: textile web - 2 resin films (or a stronger resin film) - textile web.

Another dimensioning specification for the stack structure results from the strength requirements for the three-dimensionally deformed textile material. When used as a core material for sandwich moldings, it must have a certain minimum compressive strength. When crosslinking resins are used, this requirement is generally to be met if the ratio of the square meter weight of the textile material to the weight of the resin used per square meter (corresponding to the square meter weight of the resin film) is in the range from 1: 0.25 to 1: 4, preferably 1: 0.5 to 1: 2. In the case of stacks of several layers of textile material and several layers of resin films, the sums of the square meter weights of the textile material and the resin films must of course be taken into account.

As already mentioned above, it may also be desirable in special applications to increase the amount of resin compared to the usual amounts. On the other hand, when using special techniques in the production of sandwich moldings, it may also be sufficient to use less resin, based on the textile material, so that the resin matrix does not include the entire fiber material, but that the dimensional stability of the deformed stack is ensured. Such molded articles produced with a low resin coating can be processed into high-strength sandwich articles by gluing with cover layers if the molded articles are glued with a liquid or pasty adhesive and are wetted beforehand with a liquid which also serves as a solvent and / or wetting agent for the adhesive. It can be observed here that the adhesive rises in the latticework of the network-structured shaped bodies and additionally reinforces them after curing. Without wetting, the adhesive does not rise up on the wall. An increase in the pressure and shear strength of the sandwich body can also be achieved in this way by using hydrophilic special hardeners which are known to the person skilled in the art.

Stacks with layers of different textile materials can also be used for special applications. It is thus possible to also insert, for example, nonwovens between at least 2 layers of the deep-drawable textile materials described above and to distribute the resin films between these textile webs in the manner described above. It is also possible to use the fiber material of the textile To vary planar structures, for example combinations of textile webs made of organic and inorganic fibers, such as glass fibers, can also be used.

Particularly preferred stacks consist of one or two textile webs, preferably knitted fabrics made of high-strength polyester fibers and one or two resin films in a suitable sequence.

The stack is heated in a deep-drawing mold to a temperature at which the resin becomes flowable, then drawn into the desired three-dimensional shape, and held at this temperature at a temperature at which the resin can cure until the curing process of the Resin is completely or at least so far that the deep-drawn material remains dimensionally stable. When using a thermoset, this condition can already exist even if the curing is not yet complete. In this case, it may be advantageous for economic reasons to fully harden the mold by tempering it outside the deep-drawing tool, e.g. by heat treatment for approx. 10 minutes at 160 to 200 ° C in a drying oven. In the flow phase, the liquefied resin (matrix material) envelops the fiber material of the textile fabric.

The temperature at which the uncrosslinked resin melts is generally 100 to 250 ° C., preferably 140 to 200 ° C. Within this range, the temperature should be selected so that the fiber material is evenly enclosed in the resin matrix. The curing time of crosslinking resins in this temperature range is 2 to 5 minutes. After the curing time has expired, the three-dimensionally deformed textile material can be removed from the molding tool. Instead of one crosslinking resin, a thermoplastic is used, so the thermoforming tool must first be kept at the temperature at which the thermoplastic flows in order to ensure the embedding of the fiber material in the polymer matrix. The closed drawing tool is then cooled and left in the closed state until the matrix resin has solidified again completely or at least to the extent that the deep-drawn material remains dimensionally stable.

Particularly preferred embodiments of the method according to the invention are those in which several of the preferred features mentioned above are implemented.

The three-dimensionally deformed textile material produced according to the invention can be used in a manner known per se, as has been described in detail, for example, in European Patent No. 158 234, for the production of sandwich bodies. One or more layers of the three-dimensionally deformed material can be used as the core for the sandwich structure, wherein the core layers can either be arranged one above the other or - as described in the cited document - interlocking. To produce the sandwich structure, the core material is provided on both sides with relatively thin, solid cover layers. The cover layers are usually attached to the core material by means of suitable known adhesives, in particular by means of crosslinking polymer adhesives. FIG. 2 illustrates an embodiment of such a sandwich body (4). In an oblique view, it shows such a material with a lower cover layer (5), a partially removed upper cover layer (6) and the dimensionally stable, three-dimensionally deformed textile material (1) glued in between the cover layers as a core.

Suitable outer layers for the sandwich moldings which can be produced are all outer panels which have also been used for sandwich constructions, such as aluminum or steel sheets, but in particular synthetic resin laminates with inlays, for example made of fabrics, made of carbon or glass threads. In simpler cases, plywood or hardboard, for example, are also suitable as cover layers. For the production, the core material produced according to the invention is arranged between the two cover layers provided on the inside with the adhesive material, and the sandwich obtained in this way is bonded under slight pressure, if appropriate at elevated temperature.

The following exemplary embodiment serves to illustrate the method according to the invention.

Example:

A section measuring 15 x 30 cm edge length of a knitted fabric with a basis weight of 260 g / m² made of high-strength polyester continuous yarn ( ^(R) Trevira high-strength) is covered with a commercially available 0.15 mm thick, carrier-free epoxy resin film ( ^(R) Structufilm R 382 from Hexcel SA) basis weight 150 g / m², covered in the size 15 x 30 cm and the stack obtained in this way placed in a deep-drawing tool preheated to 200 ° C. which is equipped with male and female dies made of chromium-nickel steel. The matrix has a square pattern of round holes with a diameter of 1.5 cm and a center-to-center distance of 2.2 cm and a male with a square arrangement of 2 cm high round punches with a diameter of 1 cm and a center-to-center distance of 2.2 cm, the male punches being centered with respect to the female holes.

The tool is closed at a working temperature of 200 ° C and held at this temperature for 3 minutes.

The three-dimensionally deformed material obtained is then removed.

The deep-drawn textile material produced in this way has a regular arrangement of a large number of thimble-like, approx. 2 cm high bumps with a flat plateau at a distance of 2.2 cm on a base and shows an open, filigree structure throughout. It is ideally suited as a core material for the production of sheet-like sandwich bodies. A sandwich panel manufactured using this deformed textile material as the core and two 1.5 mm thick plywood panels as cover layers has a compressive strength of 0.4 N / mm².

Claims (11)

1. A process for producing a dimensionally stable, three-dimensionally shaped, resin-coated, sheet-like textile material, characterized in that one or more layers of a thermoformable textile material and one or more resin films are stacked on top of one another and the stack at a temperature at which the resin becomes flowable Thermoforming into the desired shape, adjusting the temperature so that the resin can harden, and holding the molded stack in this shape until the resin is fully or sufficiently hardened. 2. The method according to claim 1, characterized in that the thermoformable textile material has a high elastic extensibility. 3. The method according to at least one of claims 1 and 2, characterized in that the deep-drawable textile material is a knitted fabric. 4. The method according to at least one of claims 1 to 3, characterized in that the deep-drawable textile material is made from a synthetic fiber continuous or staple fiber yarn or from glass filaments. 5. The method according to at least one of claims 1 to 4, characterized in that the thermoformable textile material is made of a polyester yarn. 6. The method according to at least one of claims 1 to 5, characterized in that the resin film consists of a thermosetting resin. 7. The method according to at least one of claims 1 to 6, characterized in that the resin film consists of an epoxy resin, phenolic resin or melamine resin. 8. The method according to at least one of claims 1 to 7, characterized in that the number of textile layers and resin films in the stack is dimensioned such that the ratio of the sum of the basis weights of the textile layers to the sum of the basis weights of the resin films in the range of 1: 0, 25 to 1: 1. 9. The method according to at least one of claims 1 to 8, characterized in that the sequence of the textile and resin layers in the stack is designed so that the resin completely penetrates the textile material during the flow period. 10. The dimensionally stable, three-dimensionally deformed, resin-coated sheet-like textile material produced by the method of claim 1. 11. Use of the dimensionally stable, three-dimensionally molded, resin-coated, sheet-like textile material produced by the method of claim 1 for the production of sheet-like sandwich bodies.

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